Method of manufacturing a connecting rod made from composite material

ABSTRACT

A method of making a connecting rod made of composite material, especially for internal-combustion engines, the composite material being formed by a reinforcement embedded in a cured material, and the connecting rod (A) comprising, along the longitudinal extension (X-X) of the connecting rod, a central shank (B) extended respectively, at its two ends, by a connecting-rod big end (C) and a connecting-rod small end (D). The connecting rod (A) is produced entirely as a single component made of composite material and the reinforcement of the composite material comprises superposed plies of crossed straight filling yarns, the filling yarns, which extend parallel to the longitudinal extension (X-X) of the connecting rod (A), constituting at least twice the volume percentage of the filling yarns which extend in each of the directions other than the longitudinal extension (X-X) of the connecting rod (A), and binding yarns which pass through the superposed plies.

This is a divisional of U.S. Ser. No. 08/720,213 filed Sep. 26, 1996,which is a continuation of U.S. Ser. No. 08/412,745 filed Mar. 29, 1995,now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a connecting rod made of compositematerial, especially for--internal-combustion engines, as well as to amethod for manufacturing such a connecting rod.

Such a connecting rod is an elongate component which includes, inaddition to a central shank, a wider big end, which is the part of theconnecting rod lying on the crankshaft side, and a narrower small end,which is the part of the connecting rod lying on the piston side. Inorder to mount it, the big end must be able to open, and it thereforeincludes two elements fastened by two bolts which exert a significantstress on that surface of the element against which they are tightened.The connecting rod is a component which has a preferential direction ofloading and has to have a high stiffness preventing deformations aroundthe bores of the small end and the big end.

A connecting rod made of composite material is already known, forexample from Patent FR-A-2,654,483. By composite material is meant amaterial which includes a reinforcement of yarns or fibers, thisreinforcement being embedded in a matrix of cured synthetic material.Such a composite material, in addition to the weight saving that itprovides, withstands mechanical loads extremely well, has a highcorrosion resistance and excellent high-temperature behavior. However,in Patent FR-A-2,654,483, these properties of composite materials arenot fully exploited on account of the fact that, in this case, theshank, small end and big end of the connecting rod are produced in theform of separate components connected by adhesive bonding and winding ofa yarn, forming a strap. Furthermore, such a production is complicatedand has to be implemented in several steps, thereby preventing effectivemass production of such connecting rods.

SUMMARY OF THE INVENTION

The object of the present invention is to avoid these drawbacks andrelates to a connecting rod made of composite material, the structure ofwhich makes it possible, on the one hand, to fully exploit theproperties of the composite materials and, on the other hand, tomanufacture a large number of such components easily and quickly.

For this purpose, the connecting rod made of composite material,especially for internal-combustion engines, said composite materialbeing formed by a reinforcement embedded in a cured material, and saidconnecting rod comprising, along the longitudinal extension of theconnecting rod, a central shank extended respectively, at its twoextremities, by a connecting-rod big end and a connecting-rod small end,is noteworthy in that, according to the invention, said connecting rodis produced entirely as a single component made of composite material,in that the reinforcement of said composite material comprisessuperposed plies of crossed straight filling yarns, the filling yarns,which extend parallel to the longitudinal extension of the connectingrod, constituting at least twice the volume percentage of the fillingyarns which extend in each of the directions other than the longitudinalextension of the connecting rod and in that binding yarns pass throughsaid superposed plies.

Thus, the reinforcement of the connecting rod made of composite materialaccording to the invention has an increased strength in the maximum loaddirection, that is to say the longitudinal extension of the connectingrod, and, in addition, since the connecting rod is made of a singlecomponent of composite material, it is simple to manufacture and theproperties of the composite material may be exploited to the maximum.

Advantageously, assuming that the filling yarns of the reinforcementextending parallel to the longitudinal extension of the connecting rodare the 0° direction yarns, the other filling yarns of the reinforcementextend along the 45°, 90° and 135° directions.

In particular, the reinforcement may comprise as many 0° directionfilling yarns as there are filling yarns extending along the otherthree, 45°, 90° and 135°, directions.

Preferably, with respect to the total volume of the composite materialincluding the reinforcement and the cured matrix, the volume percentageof the filling yarns is between 40% and 60% and the volume percentage ofthe binding yarns is between 1% and 10%.

In particular, the volume percentage of the 0° direction filling yarnsis at least substantially equal to 27%, while the volume percentage ofthe 45°, 90° and 135° direction filling yarns is at least substantiallyequal, in each case, to 9%.

Moreover, the volume percentage of the binding yarns may be at leastsubstantially equal to 3%.

Advantageously, for each series of plies, the filling yarns are arrangedin the following sequence: 0° direction yarns, 45° direction yarns, 0°direction yarns, 90° direction yarns, 0° direction yarns and 135°direction yarns.

According to another characteristic of the invention, additional 90°direction filling yarns are provided in the region of the connecting-rodbig end, increasing its thickness.

Preferably, said additional 90° direction filling yarns are incorporatedin each of said series of plies.

According to yet other characteristics of the invention, 0° directionfilling yarns, going around the connecting-rod small end, may beincorporated between said series of plies, and/or yarns, going aroundthe connecting-rod small end, may be arranged by stitching along theedges of said connecting-rod small end.

The present invention also relates to a method for manufacturing aconnecting rod made of composite material, which has just beendescribed, noteworthy in that, according to the invention:

a) a reinforcement for a sheet of composite material is produced, saidreinforcement comprising superposed plies of crossed straight fillingyarns, the filling yarns, which extend parallel to a first direction,constituting at least twice the volume percentage of the filling yarnswhich extend in each of the other directions, and binding yarns passingthrough said superposed plies;

b) said reinforcement is impregnated with a synthetic material intendedto form the matrix of said sheet of composite material;

c) said synthetic resin is cured so as to form said sheet of compositematerial;

d) said sheet of composite material is cut so as to obtainconnecting-rod preforms, said first direction corresponding to thelongitudinal extension of said preforms; and

e) each connecting-rod preform thus obtained is machined into its finalstate.

In particular, assuming that the filling yarns of the reinforcementextending along said first direction are the 0° direction yarns, theother filling yarns of the reinforcement extend along the 45°, 90° and135° directions.

Preferably, in step a), as many 0° direction filling yarns are laid downas there are filling yarns extending along the other three, 45°, 90° and135° directions.

Advantageously, for each series of plies, the filling yarns are laiddown according to the following sequence: 0° direction yarns, 45°direction yarns, 0° direction yarns, 90° direction yarns, 0° directionyarns and 135° direction yarns.

According to another characteristic of the invention, in step a),additional 90° direction filling yarns are laid down in the regioncorresponding to the connecting-rod big ends.

Preferably, in this case, said additional 90° direction filling yarnsare laid down at the time of production of each of said series of plies.

According to yet another characteristic of the invention, between saidseries of plies, 0° direction filling yarns, going around the placesprovided for the connecting-rod small ends, are laid down.

In particular, step d) may be carried out before steps b) and c) inorder thus to make it possible, after step d), to stitch yarns into thereinforcement, going around the connecting-rod small end, along theedges of the latter.

DESCRIPTION OF THE DRAWINGS

The figures of the appended drawing will make it well understood how theinvention may be realized. In these figures, identical referencesdesignate similar elements.

FIG. 1 is a front view of a connecting rod produced according to theinvention.

FIG. 2 is a side view of FIG. 1.

FIG. 3 is a view from above of a sheet from which the connecting rods ofthe invention are cut out.

FIG. 4 is the IV--IV cross section of FIG. 3.

FIGS. 5A-5F illustrate the various phases in the formation of a seriesof plies of yarns according to the invention.

FIG. 6 shows the stitching of the superposed plies.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 2 show a connecting rod A made of composite material,according to the invention, especially for internal-combustion engines.As already indicated, the composite material in question is formed by areinforcement of yarns (especially carbon, glass or boron yarns) whichis embedded in a matrix of cured synthetic material. It will be notedthat, for reasons of illustration, the network of yarns of thereinforcement is shown diagrammatically in FIGS. 1 and 2, this networkobviously not being visible as clearly when the reinforcement isembedded in the matrix.

Conventionally, the connecting rod A comprises, along its longitudinalextension X-X, a central body B respectively extended, at its twoextremities, by a connecting-rod big end C and a connecting-rod smallend D, each including a bore E1, E2 for connecting the connecting rod,on the one hand, to the crankshaft and, on the other hand, to thepiston. In order to mount it, the connecting-rod big end C must be ableto open and therefore includes two elements C1, C2 fastened by bolts(not depicted) and having, for this, internal threads G, H. As alreadyindicated, such a connecting rod is a component having a preferentialload direction (its longitudinal extension X-X), and must have highstiffness preventing deformations around the bores of the small end andthe big end.

According to the invention, the connecting rod A is produced entirely asa single component made of composite material and the reinforcement 1 ofthe composite material comprises superposed plies of crossed straightfilling yarns, the filling yarns, which extend parallel to thelongitudinal extension X-X of the connecting rod A, constituting atleast twice the volume percentage of the filling yarns which extend ineach of the directions other than the longitudinal extension X-X of theconnecting rod and, moreover, binding yarns F passing through saidsuperposed plies, forming stitches 7 having open loops 8 (FIG. 6) usinga needle, not depicted in FIG. 6. The production of a series of plies Nwill be described in detail hereinbelow with regard to FIGS. 5A-5F. Byseries of plies is meant a repeated succession of plies, as explainedhereinafter.

With respect to the total volume of the composite material, includingthe reinforcement and the cured matrix, the volume percentage of thefilling yarns is between 40% and 60% and the volume percentage of thebinding yarns is between 1% and 10%. For example, assuming that thefilling yarns of the reinforcement extending parallel to thelongitudinal extension of the connecting rod are the 0° direction yarnsand that the other filling yarns of the reinforcement extend along the45°, 90° and 135° directions, the reinforcement comprises as many 0°direction filling yarns as there are filling yarns extending along theother three, 45°, 90° and 135°, directions.

By way of example, the volume percentage of the 0° direction fillingyarns is at least substantially equal to 27%, while the volumepercentage of the 45°, 90° and 135° direction filling yarns is at leastsubstantially equal, in each case, to 9%. As regards the volumepercentage of the binding yarns, this may be at least substantiallyequal to 3%.

In order to manufacture the connecting rod A made of composite materialaccording to the invention, the procedure is generally carried out inthe following way:

a) a reinforcement is produced for a sheet of composite material, saidreinforcement comprising superposed plies of crossed straight fillingyarns, the filling yarns, which extend parallel to a first direction,constituting at least twice the volume percentage of the filling yarnswhich extend in each of the other directions, and binding yarns passingthrough said superposed plies;

b) said reinforcement is impregnated with a synthetic material intendedto form the matrix of said sheet of composite material;

c) said synthetic resin is cured so as to form said sheet of compositematerial;

d) said sheet of composite material is cut so as to obtainconnecting-rod preforms, said first direction corresponding to thelongitudinal extension of said preforms; and

e) each connecting-rod preform thus obtained is machined into its finalstate.

FIGS. 3 and 4 show such a sheet P from which connecting rods A accordingto the invention will be cut out. It may be seen, especially in FIG. 3,that the shape of the connecting rods and the formation of a sheet ofsimple geometrical shape make it possible to manufacture, simply, alarge number of connecting rods with a minimum of scrap.

FIGS. 5A-5F illustrate various phases in the formation of a series ofplies N of yarns according to the invention. In this example, for eachseries of plies, the filling yarns are laid down in the followingsequence: 0° direction yarns 4 (FIG. 5A), 45° direction yarns 4 (45)(FIG. 5B), 0° direction yarns 4 (FIG. 5C), 90° direction yarns 5 (FIG.5D), 0° direction yarns 4 (FIG. 5E) and 135° direction yarns 5 (135)(FIG. 5F). The filling yarns are laid down or a support 6, assuming thatthe series of plies in question, for reasons of clarity of the drawing,is the first series of plies that is laid down. The above yarns may belaid down in any known manner, but advantageously as described in theFrench patent applications, filed on Apr. 18, 1994, in the name of theApplicant Company for "Method and machine for the production of areinforcement for a component of composite material" and "Method andmachine for the production of a reinforcement in the form of a sheet fora component of composite material".

It will be noted that the thickness of a series of plies, that is to saythe thickness of the layer constituted by the filling yarns inserted inthe various directions defined hereinabove, depends on the laydownspacing of the yarns and on the cross section of the yarns. By way ofpractical example, this thickness is approximately 1 mm and such seriesof plies will be superposed as many times as necessary depending on thethickness of the component to be obtained.

Moreover, in order to increase the thickness of the connecting rod inthe regions L1 (FIG. 3) corresponding to the connecting-rod big ends,additional 90° direction filling yarns 5A are laid down, when making upeach series of plies, in said regions as well as in the transitionregions L2. This makes it possible to obtain directly, at thecutting-out stage, a component having a variable thickness, avoidinghaving to machine the component faces in order to achieve this.

In addition, between two successive series of plies, it is possible tolay down 0° direction filling yarns 4A going around the places providedfor the connecting-rod small ends (FIG. 3).

This may be carried out by yarn-guiding pins in the support which areremoved during the stitching operation (laydown of the binding yarns).

It is also possible, after cutting the sheet into elementary componentsand before impregnating with the matrix, to strengthen theconnecting-rod small end with yarns I stitched into the reinforcement,going around the connecting-rod small end D, along the edges of thelatter (FIGS. 1 and 2).

For implementing the method which has just been described, it ispossible to use a programmable machine, particular embodiments of whichare described in the French patent applications mentioned hereinabove.

For the plies whose yarns have simple straight paths, the machineoperator uses the callup, by means of a main program, of thesedirections.

A first program creates the data necessary for simple ply filling inaccordance with a tool. The operator inputs into this program the tooldata: length, width, spacing of the peripheral pins.

This program creates, on a floppy disk:

four files for the 0° direction,

four files for the 90° direction,

two files for the 45° direction,

two files for the 135° direction.

In fact, the 0° and 90° direction plies may be produced by starting fromone of the four corners of the tool, whereas the 45° and 135° directionplies can only start from two opposite corners.

For a particular component, the operator creates a program whichsuccessively calls up the various plies to be inserted, satisfying theconcatenation of starting and finishing points.

Moreover, one particular program will create the files corresponding tothe laydown of plies of yarns in directions other than those mentionedhereinabove.

The paths of particular yarns are generally sufficiently simple to beprogrammed by the operator, by a teaching process, these then beingcalled up by the main program.

The stitching function is called up by the stitching program. During theexecution of each stitch, the length of yarn used is measured andcompared to the required length written into the stitching program.

In order to produce the sheet, after having placed the desired fillingframe on the machine, the operator inserts the floppy disk correspondingto the frame used into the machine's floppy-disk reader, and calls upthe main program defining this sheet.

He inserts the yarns into the laydown tool and adhesively bonds theirextremities to the frame with an adhesive tape.

The filling is performed automatically and requires the intervention ofthe operator:

only after executing a pattern of six plies (a series of plies) in thecase of use of a frame with straight peripheral pins, this requiring theyarns to be packed onto these pins,

or in the event of the machine detecting the absence of yarn (emptybobbin).

At the end of filling, the operator also adhesively bonds theextremities of the yarns to the frame.

The stitching is performed after having placed, on the face opposite thestitching tool, a soft material capable of allowing the extremity of theneedle to pass through. This stitching may be performed on one face andthen the sheet may be turned over in order to be stitched on the secondface. The stitches may be produced so as to be located at the mostjudicious places for the strength of the component, in particular thetwo sides of the holes of the bolts connecting the connecting-rod bigend to the shank.

Each component may be cut out from the sheet before impregnation. Thisis essential in order to be able to arrange yarns I going around thesmall end, by stitching along the side faces (edges). This cutting-outis performed by sawing or by using a water-jet machine.

These components are impregnated according to the cycle:

putting the component in a mold,

evacuating the mold,

injecting the resin,

raising the temperature, holding the pressure until the resin has set,

demolding the preform, and

postcuring in an oven, outside the mold.

The machining is identical to that of any mechanical component. Ingeneral, it is performed with diamond grinding wheels. In the case wherethe component is produced from a sheet with the thickness variationsprovided during filling and the impregnation is performed in a mold tothe desired dimensions, machining may be reduced to separating the bigend into two elements, and to drilling the holes and cutting theinternal threads for the fixing bolts.

What is claimed is:
 1. A method for manufacturing an elongatedconnecting rod made of composite material and having a central body (3)respectively extended at its two extremities by a connecting-rod big end(C) and a connecting-rod small end (D), the method comprising the stepsof:a) producing a reinforcement sheet (P) comprising superposed plies ofcrossed straight filling yarns, some of said filling yarns extendingparallel to a first direction and some of said filling yarns extendingparallel to other directions, the filling yarns extending parallel tothe first direction constituting at least twice the volume percentage ofthe filling yarns extending in each of said other directions, andbinding yarns passing through said superposed plies, said reinforcementsheet (P) having:at least one thickened region (L1) obtained by layingdown additional filling yarns (5A) when making said superposed plies,and additional filling yarns (4A) of said first direction going aroundsaid connecting-rod small end (D), said additional filling yarns (4A)being laid down when said superposed plies are made; b) cutting out atleast one connecting-rod preform from said reinforcement sheet (P), thelongitudinal extension (X-X) of said preform corresponding to said firstdirection and at least one connecting-rod end (C, D) of said preformcorresponding to said at least one thickened region (L1); c) stitchingstrengthening yarns (I) into said preform, said strengthening yarns (I)going around said connecting-rod small end (D); d) impregnating saidpreform with a polymerizable synthetic material; e) curing said preformimpregnated with said synthetic material; and f) machining said curedpreform into the final state of said connecting-rod.
 2. The method asclaimed in claim 1, wherein said filling yarns of said reinforcementsheet which extend along said first direction comprise 0° directionfilling yarns and wherein said filling yarns of said reinforcement sheetwhich do not extend along said first direction comprise 45°, 90° and135° direction filling yarns.
 3. The method as claimed in claim 2,wherein as many of said 0° direction filling yarns (4) are laid down asthere are 45°, 90° and 135° direction filling yarns.
 4. The method asclaimed in claim 3, wherein for each series of superposed plies, thefilling yarns are laid down according to the following sequence: said 0°direction yarns, said 45° direction yarns, said 0° direction yarns, said90° direction yarns (5), said 0° direction yarns (4) and said 135°direction yarns.
 5. The method as claimed in claim 3, wherein in step a)said additional filling yarns (5A) extend along the 90° direction.